1. Field of the Invention
This invention is directed to sealing joints for mated bodies. In a particularly preferred embodiment the invention is directed to a pressure-actuated joint, especially a pressure-actuated joint of a solid rocket motor, such as a reusable solid rocket motor.
2. State of the Art
Reusuable solid rocket motor (RSRM) designs can be found in many rocketry applications, with perhaps the best known application involving the two solid rocket boosters of the Space Shuttle. The solid rocket boosters of the Space Shuttle are attached to opposite sides of a main external tank of the Space Shuttle. On the launch pad, the two solid rocket boosters, and in particular the cases of the boosters, structurally support the entire weight of the external tank and orbiter and transmit the weight load through their structure to the mobile launch platform. Together, the solid rocket boosters furnish the majority of the thrust required to launch the Space Shuttle from its mobile launch platform and contribute to accelerate the vehicle to more than about 4800 km per hour (3,000 miles per hour) before detaching and separating from the external tank.
FIG. 1 illustrates an example of an RSRM of the Space Shuttle vehicle. The RSRM is generally designated by reference numeral 10 in FIG. 1. The RSRM 10 comprises a plurality of detachable segments connected to each other by field joints 12 and factory joints 14, as identified in FIG. 1. The term xe2x80x9cfield jointxe2x80x9d is commonly used in the field of rocketry to denote joints capable of being assembled in either a factory or the field. The field joints 12 and segmented design provides maximum flexibility in transportation, handling, recovery, refurbishment, assembly, and fabrication of the RSRM 10. For example, the segmenting of the solid rocket motor facilitates propellant casting procedures and permits transportation of the large segments on heavy-duty railcars incapable of carrying the assembled RSRM 10.
FIG. 2 illustrates the major segments of each RSRM 10 of the Space Shuttle vehicle by depicting the RSRM 10 in an exploded view. Proceeding from the forward end to the aft end of the RSRM 10, the RSRM 10 comprises a nose cap 30, a frustum forward cap 32 containing forward separation motors, a forward skirt 34, a forward segment 20, a forward-center segment 22, an aft-center segment 24, an aft segment 26, an exit cone 36, and an aft skirt 38. The forward segment 20, forward-center segment 22, aft-center segment 24, and aft segment 26 each contain a solid propellant grain structure, which is illustrated as a center-perforated propellant grain structure 40. The forward segment 20 also contains an igniter assembly (not shown in FIGS. 1 and 2) installed at the forward end of the center-perforated propellant grain structure 40.
The RSRM 10 includes an outer case (unnumbered in FIGS. 1 and 2) that surrounds the center-perforated propellant grain structure 40. Like the propellant grain structure 40, the outer case is also of a segmented design. In particular, each of the segments 20, 22, 24, and 26 has a corresponding annular outer case segment containing a segmented portion of the propellant grain structure 40. Although not apparent from FIGS. 1 and 2, interposed radially between the propellant grain structure 40 and each of the outer case segments are insulation and liner layers. The insulation layer protects the outer case from the heat and particle streams generated during combustion of the propellant grain structure 40. The liner bonds the propellant grain structure 40 to the insulation and/or any non-insulated portions of the outer case. In addition to its adhesive function, the liner may also serve the additional functions of inhibiting an approaching flame front of the burning propellant grain 40 and contributing to the prevention of leakage of combustion gases or liquid to the outer case.
Special precautions must be taken at the field joints 12 between connected segmentsxe2x80x94i.e., segments 20 and 22, segments 22 and 24, and segments 24 and 26xe2x80x94to prevent hot combustion gases from escaping past the insulation and reaching the outer case. Penetration of the combustion gases through the insulation can create an extremely hazardous condition.
Thus, there is a strong interest in the art, as well as public interest, to continue improving upon the field joints of a rocket motor, especially rocket motor components of manned vehicles, such as the RSRM""s of the Space Shuttle.
It is therefore one of the objects of this invention to provide a pressure-actuated joint system suitable for establishing a sealed joint at the interface of two mated bodies. In regards to this object, it would be especially advantageous to provide a pressure-actuated joint system suitable for use in pressure vessels generating high internal pressures, such as rocket engines.
It is a further object of this invention to provide a pressure vessel comprising a plurality of segments, in which at least one of the interfaces between segments comprises a joint, such as a field joint, sealed with the pressure-actuated joint system of this invention.
It is still a further object of this invention to provide a rocket motor, such as a reusable solid rocket motor, comprising a plurality of segments, in which at least one of the mating interfaces between the segments of the rocket motor comprises a joint, such as a field joint, sealed with the pressure-actuated joint system of this invention.
Additional objects and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations pointed out in the appended claims.
To achieve foregoing objects, and in accordance with the purposes of the invention as embodied and broadly described in this document, a pressure vessel according to a first aspect of this invention comprises an outer case structure, a first annular rubber layer, and a second annular rubber layer. The outer case structure comprises a plurality of annular case segments, the annular segments including a first case segment and a second case segment, the first case segment mating with the second case segment. The first annular rubber layer is associated with and disposed radially inboard of the first case segment. The first annular rubber layer has an interfacing surface portion. The second annular rubber layer is associated with and disposed radially inboard of the second case segment, and has a thickness defined between a radial inner surface and a radial outer surface of the second annular rubber layer. The second annular rubber layer also has a slot extending from the radial inner surface across a portion of the thickness of the second annular rubber layer to define a main body portion and a flexible portion of the second annular rubber layer. The flexible portion has an interfacing surface portion abutting against the interfacing surface portion of the first annular rubber layer and is sufficiently flexible to follow movement of the first annular rubber layer during operation of the pressure vessel. The slot is positioned for receiving pressurized gas from the pressure vessel and for establishing a pressure-actuated joint between the interfacing surface portions. At least one of the interfacing surface portions has a plurality of recesses formed therein, the recesses being enclosed and sealed by the first annular rubber layer and the flexible portion of the second annular rubber layer.
To achieve other objects, and in accordance with the purposes of the invention as embodied and broadly described in this document, a rocket motor according to a second aspect of this invention is provided. The rocket motor comprises a rocket motor outer case structure including a plurality of annular case segments. The case segments include a first case segment and a second case segment. The first case segment mates with and is positioned aft relative to the second case segment. The rocket motor further comprises a first annular insulation layer and a second annular insulation layer. The first annular insulation layer is associated with and disposed radially inward of the first case segment. The second annular insulation layer is associated with and disposed radially inward of the second case segment. The second annular insulation layer also has a thickness defined between a radial inner surface and a radial outer surface of the second annular insulation layer. A slot extends from the radial inner surface of the second annular insulation layer in an outward direction across a portion of the thickness of the second annular insulation layer to define a main body portion and a flexible (finger) portion positioned aft of the main body portion. The flexible portion of the second annular insulation layer has an aft-facing surface that abuts against an interfacing portion of a forward-facing surface of the first annular insulation layer. The flexible portion is sufficiently flexible to follow movement of the first annular insulation layer during operation of the rocket motor. Recesses are provided in the forward-facing surface of the first annular insulation layer and/or the aft-facing surface of the second annular insulation. The first annular insulation layer and the second annular insulation layer together enclose the recesses.
A combustible propellant grain structure is positioned on a radial inner surface of the first and second annular insulation layers. The propellant grain structure has a center perforation and at least one annular channel extending from the center perforation to the slot for delivering pressurized gas to the slot during propellant combustion and for establishing a pressure-actuated joint between the aft-facing surface of the flexible portion and the interfacing portion of the forward-facing surface.
To achieve other objects, and in accordance with the purposes of the invention as embodied and broadly described in this document, a rocket motor according to a third aspect of this invention is provided. The rocket motor comprises a rocket motor case structure, first and second annular insulation layers, an annular sealing insert, and a propellant grain structure. The rocket motor outer case structure comprises a plurality of annular case segments, the annular case segments including a first case segment and a second case segment, the first case segment mating with and positioned aft relative to the second case segment. The first annular insulation layer is associated with and disposed radially inward of the first case segment. The first annular insulation layer has a forward-facing surface. The second annular insulation layer is associated with and disposed radially inward of the second case segment, and has a thickness defined between a radial inner surface and a radial outer surface of the second annular insulation layer. The second annular insulation layer also has a slot extending from the radial inner surface of the second annular insulation layer in an outward direction across a portion of the thickness of the second annular insulation layer to define a main body portion and a flexible portion. The flexible portion is positioned aft of the main body portion. The flexible portion has an aft-facing surface and is sufficiently flexible to follow movement of the first annular insulation layer during operation of the rocket motor. The annular sealing insert is received by at least one of the first and second annular insulating layer and has a first surface abutting against the forward-facing surface and a second surface that is opposite to the first surface and abuts against the aft-facing surface of the flexible portion. A plurality of substantially axial passages is formed through the annular sealing insert. The forward-facing surface of the first annular insulation layer and the aft-facing surface of the second annular insulation layer seal the ends of the passages. The combustible propellant grain structure is positioned on a radial inner surface of the first and second annular insulation layers. The propellant grain structure has a center perforation and at least one annular channel extending from the center perforation to the slot. The channel delivers pressurized gas to the slot during propellant combustion and establishes a pressure-actuated joint.